1. Field of Invention
This invention relates generally to elongated structures with an internal lumen such as pacemaker leads, defibrillator leads, and catheters, that are implanted transvenously or subcutaneously; it relates more specifically to apparatus and methods for removing such structures from a body.
2. Prior Art
Medical devices are chronically implanted to provide a variety of therapies to patients. Common examples are implantable pacemakers and defibrillators that monitor cardiac activity and deliver electrical therapy. Another example is an implantable drug pump that delivers pharmacological therapy. Because of the required size of such devices, they are usually placed subcutaneously or submuscularly in locations that maximize such factors as patient comfort and ease of implant. Monitoring and therapy usually occur at an anatomical location some distance from the device implant site, and this is routinely accomplished through the use of flexible elongated structures such as leads or catheters connected to the device. This arrangement has been widely accepted, in part, because leads and catheters allow for techniques such as transvenous introduction and minimally invasive subcutaneous tunneling, which are recognized for ease of use at implant and for limiting patient discomfort.
Transvenous pacemaker and defibrillator electrical leads typically are constructed with a flexible polymer body using materials such as silicone or polyurethane, with one or more internal lumens that extend the length of the lead. These lumens are used to place electrical conductors through the lead, allowing electrical connection between a medical device at the proximal end of the lead and the electrodes located at various positions along the lead and particularly at the distal end. At least one of these electrical conductors is typically a flexible multifilar coil that extends the length of the lead. The hollow center of the coil provides a pathway for temporary introduction of a wire stylet that aids in implanting the lead by providing stiffness and allowing shaping of the lead.
Although the expected life of an implanted transvenous lead is many years, removal is sometimes required due to mechanical or electrical failure, or changes in patient condition. Nonfunctional leads left in place can interfere with the placement and function of new leads, act as a conduit for infections, interfere with normal physiological functions such as cardiac valve function and compromise venous patency. Particularly for chronically implanted transvenous leads, removal can be difficult due to encapsulation or attachment of the surrounding tissue to the lead resulting from the natural physiological response to a foreign body. Removal is often made more difficult by design features of the lead that are intended to provide fixation, such as outwardly protruding tines at the distal portion of the lead or a helical screw at the distal end.
In some cases, extraction of a chronically implanted transvenous lead requires surgical removal; but often a lead can be successfully removed by the use of traction forces applied to the lead, or a combination of traction forces and excising sheaths that are advanced over the surface of the lead body. Because easy access is generally limited to the proximal end of the lead, these traction forces must be applied at or near the proximal end. A major problem with this method is that when extraction forces are applied, the flexible lead body and particularly the internal coil stretch. This results in a situation where traction forces are no longer effective for lead removal, and a situation which becomes increasingly dangerous as the structural integrity of the lead is increasingly compromised. The more damaged the lead becomes, the more likely the need for surgical removal becomes for the patient's safety.
Various methods have been employed to aid in lead removal. Early methods consisted of simple traction applied to the proximal end of the structure. More recent developments include excising sheaths that are advanced over the lead body and tools that employ laser excising methods, which have been described in numerous patents and publications.
In addition, special devices have been developed to facilitate lead extraction, which are introduced into the lumen of the lead and employ various methods to engage the coil and allow traction forces to be applied. Currently, several types of these extraction devices are commercially available from several companies, most notably Cook Medical, Spectranetics and VascoMed; and designs and methods are described in existing patents.
A series of related patents and published applications assigned to Cook Pacemaker Inc. and Cook Vascular Inc. by Goode et al. (U.S. Pat. Nos. 4,988,347; 4,943,289; 5,011,482; 5,013,310; 5,207,683; 5,632,749; 6,136,005; 6,687,548; U.S. Pub. No. 2004/0116939) and Lui (U.S. Pat. No. 6,712,826; U.S. Pub. No. 2002/0010475) describes various extraction devices. U.S. Pat. Nos. 4,988,347 and 5,013,310 describe an apparatus comprising a stylet wire with a wire coil wrapped around the distal end. Rotation of the stylet unwinds the wire coil and causes it to mesh with the coil of the lead. U.S. Pat. Nos. 4,943,289; 5,011,482; 5,207,683; 5,632,749; 6,136,005; 6,687,548; and 6,712,826 also describe a stylet wire with a wire coil wrapped around it that is unwound by rotation of the stylet wire. In addition, these patents describe embodiments that include: a flexible tube through which a fluid is passed to expand a balloon on the distal end; a flexible tube with strips cut in the distal end, which is expanded by means of an actuator rod inserted into the tube; a flexible tube with a series of barbs or a ridge, which is expanded by insertion of an actuator rod; a flexible tube with a slotted sleeve at the distal end, which is expanded by movement of an actuator rod; a flexible tube with an expandable sleeve of pliable material at the distal end, which is expanded by movement of an actuator rod; a flexible tube with a cylindrical rod at the distal end that is rotatable to an off-centered position; and a hollow tube with an extended projection at the distal end that is manipulated by insertion of a stylet. In addition, U.S. Pat. Nos. 6,136,005; 6,687,548; and 6,712,826 also describe a hollow tube and a stylet with a folded-back portion at the distal end or laterally flexible member attached to the distal end that acts as a hook to engage the lead coil. In addition, U.S. Pat. Nos. 6,687,548 and 6,712,826 and U.S. Publications 2004/0116939 and 2002/0010475 also describe a stylet pull wire with an expandable portion comprising multifilar helically wound or parallel wires that are compressed and expanded by advancement of an actuator portion such as a cannula or coiled wire.
A series of related patents assigned to Spectranetics Corp. by Coe et al. (U.S. Pat. Nos. 6,167,315; 6,324,434 B2; 6,772,014 B2) describes various designs for extraction devices. U.S. Pat. Nos. 6,167,315 and 6,324,434 B2 describe a lead engaging member that is a sheath of elastic material or braided wires, which is held in a stretched or relaxed position by manipulation of a mandrel or concentric hypotubes. These patents also describe the use of a mandrel with an attached wire coil or helical ribbon that is expanded by manipulation of the mandrel. In addition, U.S. Pat. No. 6,772,014 describes a mandrel with expansion jaws that are controlled by manipulation of the mandrel, the use of a hypotube with a series of bristles that extend radially, and a mandrel with multiple radially expandable elastic members.
Patents assigned to VascoMed by Reinhardt et al. (U.S. Pat. Nos. 6,315,781 and 6,358,256) describe extraction devices. U.S. Pat. No. 6,315,781 describes a tube with an internal cable attached to an anchoring member at the distal end. Retraction of the cable results in distortion of the distal end of the cable and displacement of the anchoring member. U.S. Pat. No. 6,358,256 describes a slotted tube that is compressed and deformed radially by exerting a tensile force on an internal control wire.
Patents assigned to VascoMed by Hocherl et al. (U.S. Pat. Nos. 5,549,615 and 5,556,424) also describe extraction devices. U.S. Pat. No. 5,549,615 describes an extractor including an elongated hollow shell; a wire located within, which is movable relative to the shell; and an extractor head attached to the end of the wire. The extractor head includes barbs that spread out radially and hook the lead lumen when the wire is pulled. U.S. Pat. No. 5,556,424 describes an extractor consisting of a guide barrel, a beveled clamping element and a pull wire joined to the clamping element. The clamping element is moved by traction force on the pull wire, resulting in expansion of the extractor at the area of the clamping element.
U.S. Pat. No. 4,574,800 by Peers-Trevarton and assigned to Cordis describes a lead extractor designed to impart a wedging condition at the distal end of an implanted lead. The lead extractor comprises a tube with a slotted distal portion that is expanded by retracting a protrusion attached to a line contained within the tube.
U.S. Pat. No. 5,769,858 by Pearson et al. and assigned to Medtronic describes a locking stylet that is designed to impart a wedging condition at the distal end of an implanted lead. The locking stylet comprises a tubular member with a distal end that is deformed by use of a pull wire.
There are several limitations of the existing extraction systems described above. Stylets with wrapped wire coils require stylet rotation which can be difficult to control, and the coils may unwind during insertion and prematurely engage the lead. Conventional systems comprising hollow tubes with balloons, expandable wire mesh, hooks or expansion jaws, and systems with pull wire activated members, can be difficult to operate correctly, and are relatively complex and expensive to manufacture. In addition, conventional systems described above are often ineffective at engaging the implanted structure sufficiently to allow the required traction. These systems result in traction forces being applied unevenly along the lead, limiting the effectiveness for lead removal, with most existing systems engaging the implanted structure only at the distal end or at one other location. While providing a means of engaging the implanted structure, these conventional systems do little to reinforce or stabilize the overall structure during application of the traction forces. Another limitation of conventional systems is that once the locking mechanism has been engaged, which often involves permanent deformation of a part, it is difficult or not possible to disengage it. This makes repositioning or removal of the extraction system difficult if it becomes necessary due to complications, potentially resulting in the need for surgical intervention.
Although it is not as common as transvenous implantation, implantable pacemaker and defibrillator leads are also implanted through tunneling techniques in subcutaneous and epicardial locations. Leads for this type of implant are similar in construction to transvenous leads with internal lumens as described above. As is true for transvenous leads, removal of leads from these locations is sometimes also necessary due to mechanical and electrical malfunction. Although the consequences of leaving abandoned leads in these locations are generally less of a concern than for transvenous leads, they are often removed for patient comfort, to eliminate or prevent infection and to eliminate interaction with other implanted devices. Conventional extraction of these leads with traction is subject to the same problems explained above for transvenous leads, and surgical removal carries similar undesirable risks of morbidity and patient discomfort.
Implantable drug pumps may also make use of chronically implanted flexible leads or catheters constructed with a hollow lumen, for physiological monitoring and for drug delivery to specific locations in the body that are remote from the device implant site. As with pacemaker and defibrillator leads, conventional extraction of these electrical leads and catheters with traction is subject to the same problems explained above, and surgical removal carries similar undesirable risks of morbidity and patient discomfort.
From the foregoing discussion, those skilled in the art will appreciate that a need exists for a means to facilitate extraction of chronically implanted leads and catheters that will obviate the cited drawbacks of those currently available. The invention of this disclosure provides such benefits with an apparatus and method of use that overcome the limitations of existing extraction devices mentioned above.